1. Field of the Invention
This invention relates to a high-molecular weight carbon material, i.e. a supermolecular carbon material and a method of forming the same, and in particular to a high-molecular weight carbon material, i.e. a supermolecular carbon material, having one-dimensional, two-dimensional or three-dimensional structure in which cylindrical high-molecular weight carbon materials having a fine tubular structure are bonded to soccer ball-like high-molecular weight carbon materials as a point of contact, and a method of forming the same.
2. Disclosure of the Related Art
With a development of high-molecular weight carbon materials, high-molecular weight carbon materials having a fine tubular structure with the nanometered order in a diameter have been recently discovered on a carbon rod after an arc discharge (S. Iijima, Nature, Vol. 354, pp. 56-58, 7 Nov. 1991).
These high-molecular weight carbon materials are formed by (a) providing benzene shell-like hexagonal molecules as a constituent unit which are formed by covalent bonding of carbon atoms, (b) placing the molecules tightly in a plane to form a carbon molecule sheet, (c) rolling the carbon molecule sheet into a cylindrical shape to form a cylindrical carbon tube as a unit or a high-molecular building block, (d) repeating the above steps (a)-(c) to form a plurality of cylindrical carbon tubes having different diameters, and thereafter (e) arranging their cylindrical carbon tubes in a concentric configuration to form a telescopic structure.
The above-mentioned cylindrical tubes have an extreme micro-diameter of the order of 1 nm at a minimum and the spacing between a cylindrical tube and its inside cylindrical tube or its outside cylindrical tube is of the order of 0.34 nm which is approximately the same as the interlayer spacing of a graphite molecule. The interaction between tubes is van der Waals type, and electron transfer from tube to tube is very small. In the above-mentioned telescopic structure, there are various kinds of structure such as a double structure, triple structure, quadruple structure, quintuple structure.
The above high-molecular weight carbon material will be hereinafter referred to in some cases as a "(carbon) nanotube" or a "(carbon) tube".
The carbon nanotube takes an almost infinite number of structures, which are characterized by the diameter and the degree of helicity. The relation between the molecular structure and electronic band structure of the carbon nanotube has been taught in Japanese Patent Application No. 56306/1992 which was laid open on Sep. 7, 1993 under Japanese Unexamined Patent Publication No. 229809/1993, the disclosure of which is hereby incorporated by reference herein. In addition, a method of fabricating carbon tube devices having desired properties on the basis of the above relation has been proposed therein.
The above Application No. 56306/1992 and N. Hamada et al., Phys. Rev. Lett., 68(10), pp.1579-1581(1992) teach that the carbon nanotubes exhibit a variety of properties in electronic conduction from a metal to a semiconductor with various band gaps, depending on the radius of the cylindrical tube and the degree of helical arrangement of the six-membered carbon rings (i.e. the carbon hexagons) and that the carbon nanotubes are useful as a material for use in functional devices utilizing such properties.
On the other hand, soccer ball-like spherical high-molecular weight carbon materials having benzene shell-like hexagonal molecules as a constituent unit or molecular building block are taught in S. Iijima et al., Nature, Vol. 356, pp. 776-778(1992), the disclosure of which is hereby incorporated by reference herein. S. Iijima et al. have shown that a variety of complex variants of carbon nanotubes are obtained by introducing pentagons and heptagons into the hexagonal network. Also, it is known that the molecules such as C.sub.60, C.sub.70, C.sub.78, C.sub.82, . . . can stably exist. These soccer ball-like spherical carbon materials are in the solid state or in the form of a face-centered cubic lattice or any other crystal structures depending on van der Waals forces. If the crystal or solid material is doped with K, Rb, Cs or the like, the doped material exhibits the metal conduction and superconductivity at low temperature.
The above-mentioned carbon nanotube and soccer ball-like material and high-molecular weight materials derived from either of them, and properties of these materials are known. However, materials obtained by combining the carbon nanotubes and the soccer ball-like materials have not been yet known and even suggested and such combination is unobvious to a person having ordinary skill in the art. Of course, properties of the combined materials are not entirely known.